Elevators having a linear motor mounted on the counterweight are known in the prior art. German Offenlegungsschrift No. 2,002,081, published Jan. 19, 1970; German Offenlegungsschrift No. 3,422,374, published Dec. 19, 1985; U.S. Pat. No. 4,402,386, granted Sept. 6, 1983; and Japanese Patent Publication No. 61-260678, published May 21, 1988 all disclose elevators with linear motors mounted on the Counterweight for providing the motive power for an elevator. The armature of the motor is a pole or rail mounted in the hoistway over which the motor will run. The use of such a linear motor drive eliminates the need for a separate motor room in the building in which the elevators are located. Such elevators are also very quiet, and thus are highly desirable from the passenger's view point.
While such elevator assemblies are highly desirable, there exist certain problems relative to the linear elevator assemblies which are disclosed in the aforesaid prior art. The above-noted German reference discloses a linear motor mounted on a counterweight assembly which motor uses the counterweight standard guide rails as its armature. One problem which arises with this approach relates to the induced magnetic flux which is required to power the elevator. Standard guide rails do not provide enough cross-sectional area to provide for the flux magnitude which is needed. Another problem with this approach relates to the desirability of coating the armature with a layer of a highly conductive metal such as aluminum or copper. This thin metal layer is desirable since it improves the efficiency of the motor. When the conductive coating or layer is applied to a guide rail, however, that guide rail then cannot be used for car stop braking or for emergency braking because the conductive coating would be worn off of the rail quickly. Using that rail to guide the counterweight movement is also undesirable because guide rollers or guide shoes can wear the coating off of the rail.
In the aforesaid U.S. Pat. No. 4,402,386, a hollow cylindrical guide rail is used in conjunction with a toroidal linear motor. The guide rail can consist of an aluminum layer coated onto a solid steel column so that sufficient rail cross-sectional area is achieved. The operating brakes are mounted on the elevator car and act upon the car guide rails. The use of the aluminum coated steel column solves the cross-sectional area problem of the German reference, but the aluminum coating is still subject to abrasion from the counterweight guide rollers. Additionally, the weight of the coated steel column limits its use to relatively low rise applications. Inclusion of safety gears on the counterweight would damage the armature once the safeties are used.
The Japanese reference proposes the use of coated conventional guide rails as a double armature for a multiple linear motor assembly mounted on the counterweight. Guide rollers contact the coated rails, and electromagnetic operational brakes are mounted on the counterweight to engage the rails. This type of arrangement will encounter the wear problems described above, and is thus undesirable. Counterweight safety gears are also ruled out as an option since they will damage the guide rail armatures if activated. The Japanese reference also shows a second embodiment which uses a flat steel plate coated with a conductive metal layer as the armature for the linear motor. Separate guide rails are used to guide movement of the counterweight in the second embodiment. Rollers contact the coated part of the armature to properly space the motor from the armature. Thus the coating can be damaged by the rollers, and the assembly is complex due to the use of the separate guide rails.